Although the briquetting and pelletizing processes are well known in the iron and steel industry, these processes have not been used successfully to recycle various steel mill waste materials with a significant iron content to the blast furnace. Historically, these waste materials, such as iron pellet fines, steelmaking slag, mill scale, blast furnace flue dust, and sludge (see Table 1 below for a more detailed description), had to be processed through a sintering step to reclaim the iron, flux, and manganese units contained therein. Sintering plants and the sintering process, however, are asserted to produce adverse environmental impact and are expensive to operate. If the material was not processed through a sintering plant, it had to be disposed of in a landfill.
TABLE #1 ______________________________________ Typical Steel Mill By-Products Percent Percent Percent Percent CaO & Waste Product Fe C SiO.sub.2 MgO ______________________________________ Steel Making 18-24 -- 10-15 &gt;40 Slag Blast Furnace 27-37 25-34 13-17 3-5 Dust Blast Furnace 25-35 27-39 14-20 2-4 Sludge Mill scale, 69-72 -- &lt;1 trace Slab Caster Mill scale, 64-69 -- &lt;1 trace Hot Strip Mill ______________________________________
The steel industry has used the cold briquetting process to briquette materials of value to be added to a basic oxygen steelmaking furnace, such as flourspar or a mixture of flourspar and mill scale. The traditional lime and molasses binder used in these briquettes cannot be used, however, to yield a briquette strong enough to allow the material to be conveyed to a blast furnace and travel gradually from ambient temperature to up to 2000.degree. F. (the softening zone of the furnace) without disintegrating into fines which would choke off the gas flow within the furnace, blanket the furnace burden, or escape into the furnace flue gas and overload the flue gas cleaning system.
The process of briquetting materials of value has been refined to use a Portland cement and molasses binder to increase the crush strength of the briquettes. See U.S. Pat. No. 3,871,869 (flourspar, ferrous metals, calcium flux, and colemanite); D. Slatter, The Use of Cement/Molasses Instead of Lime/Molasses as Binders in Briquetting Chrome Ore Fines, Proceedings of the 19th Biennial IBA Conference, pp. 237-51 (Sept. 1985). However, a process of briquetting steel mill by-product material into briquettes that are strong enough to be recycled directly into a blast furnace has not been developed.
The steel industry has also long used a pelletizing process to pelletize iron ore fines from the ore mining and benefaction process into pellets that are fed directly into the blast furnace. However, a cold process, as well as a hot process, of pelletizing steel mill by-product material into pellets that are strong enough to be recycled directly into a blast furnace has not been heretofore developed.
It would be desirable, therefore, if there were steel mill by-product material briquettes or pellets and processes of making these briquettes or pellets that resulted in a recyclable product which could be fed directly into a blast furnace, thus eliminating the need for a sintering step without adversely affecting the performance and operation of the blast furnace.